1. Field of the Invention
This invention relates to purification of gases. More particularly this invention relates to the purification of gases such as those gases emanating from the partial gasification resp. combustion of a fuel, which gases contain heavy metal compounds, by a two-stage process in which the gases are first scrubbed with a solvent to thereby form a solution of the gases and heavy metal compounds, and thereafter the resultant solution is heated at from 70.degree. to 250.degree. C. for at least 0.25 hour at a pressure higher than the vapor pressure of the solvent while the heavy metals are precipitated.
2. Discussion of the Prior Art
The invention relates to a process in which the deposition and caking of insoluble heavy metal compounds in the degasification column (also known as a regeneration unit) of a gas scrubber is prevented. An example of such a gas scrubber is one known as a Rectisol plant which is used with gases emanating from the partial gasification resp. combustion of fuels containing heavy metals.
Gas scrubbers of this kind are components of plants producing synthesis gas by the partial gasification resp. combustion of oils, oil residues, coal, or lignite, for example petroleum residue plants and plants for the destructive distillation of coal, and they serve to remove gaseous impurities, such as H.sub.2 S, HCN, COS and HSCN which hinder further catalytic processing of the resulting gases. In addition, these scrubbers also absorb those gaseous impurities such as metal carbonyls which, together with the first mentioned gaseous impurities can form insoluble compounds which form deposits in the gas scrubbers, particularly in the regeneration units thereof. The deposition and caking of these insoluble compounds in the degasification columns of the gas scrubbers can seriously reduce the operating life of the scrubber.
When solid and liquid fuels of the above types containing heavy metals, such as Visbreaker residues, are subjected to partial gasification resp. combustion and thereafter to scrubbing, and also when increased total pressures are used in these gasification plants, problems of this kind occur on an increased scale.
The present tendency is to use petroleum residues containing high proportions of heavy metals and to process them at higher total pressures. Hitherto no economical solutions have been known for preventing such caking and therefore achieving a normal operating life.
It is an object of this invention, therefore, to prevent the deposition of insoluble heavy metal compounds in the degasification columns of gas scrubbers, thereby lengthening the operating life of such scrubbers.